In the oil and gas industry, geophysical and geological prospecting techniques are commonly used to aid in the search for and evaluation of subterranean hydrocarbon deposits. Geophysical data are combined with geological data and interpreted for purposes of analysis and for presentation to decision makers. The interpretations, and the information they contain, form the basis for decisions whether and where to drill for hydrocarbons. The interpretations are comprised of representations of subterranean geological features or objects like bedding layers, fault traps, anticlines, and other features well known to practitioners in the art. For example, an interpreted bedding layer surface may be displayed as a three-dimensional object showing the layer's position in the subsurface. However, these geological objects are not merely surfaces in a subterranean space, they are also associated with a whole host of characteristics critical to decision making that are not presented in one presentation.
Display and presentation methods have been developed by related geoscience disciplines, particularly in the oil industry, because of the need to combine and present large amounts of related complex data efficiently. This background section describes the basics of seismic data acquisition and some aspects of data presentation. As will be apparent from the description of the display methods, most data displays relate primarily to a presentation of one characteristic of data, or one data characteristic associated with a subsurface position.
Generally, a seismic energy source is used to generate a seismic signal, which propagates into the earth and is at least partially reflected by subsurface seismic reflectors (i.e., interfaces between underground formations having different acoustic impedances). The reflections are recorded by seismic detectors located at or near the surface of the earth, in a body of water, or at known depths in boreholes, and the resulting seismic data may be processed to yield information relating to the location of the subsurface reflectors and the physical properties of the subsurface formations.
2-D seismic data is acquired along lines that consist of geophone arrays onshore or hydrophone streamer traverses offshore. FIG. 1, shows an example of portions of a marine seismic data acquisition system. A vessel 10 on a body of water 15 overlying the earth 16 has deployed behind it a seismic source array 20 and a streamer cable 25. The seismic source array 20 is typically made up of individual air guns (not shown) that are fired under the control a controller (not shown) aboard the vessel 10. Seismic pulses propagate into the earth and are reflected by a reflector 22 therein. Exemplary raypaths 41a, 41b from the source to the receiver are shown. For simplifying the illustration, only one reflector is shown: in reality, there would be numerous reflectors, each giving rise to a reflected pulse. After reflection, these pulses travel back to the surface where they are recorded by detectors (hydrophones) 30a, 30b, . . . , 30n in the streamer cable. The depth of the source array and the streamer cable are controlled by auxiliary devices (not shown). In acquiring a line of seismic data, the vessel 10 travels in the water and periodically fires the airgun 20 at different source locations. Data corresponding to each such source location are recorded by the plurality of receivers.
The acquisition geometry for a full 3-D data set on land is illustrated in FIG. 2 wherein, within a region 119, sources 124 are deployed along a plurality of source lines 126a, 126b. . . 126n and data are recorded by receivers 122 along receiver lines 120a, 120b. . . 120n nominally defining an inline direction. In conventional processing, data from the plurality of sources and receivers are output into bins such as 121. With this high density coverage, extremely large volumes of digital data need to be recorded, stored and processed before final interpretation can be made. Processing requires extensive computer resources and complex software to enhance the signal received from the subsurface and to mute accompanying noise which masks the signal.
3-D marine seismic data may be acquired (not shown) by using a plurality of widely spaced parallel streamers recording energy that has been generated by a number of seismic sources that are spaced apart in the cross-line direction. Once the data is processed, geophysical staff compile and interpret the 3-D seismic information in the form of a 3-D cube which effectively represents a display of subsurface features. Using the data cube, information can be displayed in various forms. A commonly used display comprises horizontal time or depth slice maps can at selected locations within a data volume. Using a computer workstation an interpreter can slice through the field to investigate reservoir issues at different horizons. Vertical slices or sections can also be made in any direction using seismic or well data. Time maps can be converted to depth to provide a structural interpretation at a specific level.
Seismic data has been traditionally acquired and processed for the purpose of imaging seismic reflections. Changes in stratigraphy and structure are often difficult to detect on traditional seismic displays due to the limited amount of information that seismic data contain in a cross-section view. Although 3-D views provide an opportunity to see a much larger portion of these features, it is difficult to identify fault surfaces within a 3-D volume where no fault reflections have been recorded.
U.S. Pat. No. 5,563,949 to Bahorich et al teaches dividing the three-dimensional volume into a plurality of vertically stacked and generally spaced apart horizontal slices; dividing each of the slices into a plurality of cells; measuring across each of the cells the cross-correlation between one pair of traces lying in one vertical plane to obtain an in-line value and measuring the cross-correlation between another pair of traces lying in another vertical plane to obtain a cross-line value that are estimates of the time dip in an in-line direction and in a cross-line direction; combining the in-line value and the cross-line value to obtain one coherency value for each of the cells; and displaying the coherency values of the cells across. Such a coherency display is particularly well suited for interpreting fault planes within a 3-D seismic volume and for detecting subtle stratigraphic features in 3-D. This is because seismic traces cut by a fault line generally have a different seismic character than traces on either side of the fault. Measuring trace similarity, (i.e., coherence or 3-D continuity) along a time slice reveals lineaments of low coherence along these fault lines. Such coherency values can reveal critical subsurface details that are not readily apparent on traditional seismic sections. Also by calculating coherence along a series of time slices, these fault lineaments identify fault planes or surfaces.
U.S. Pat. No. 5,892,732 to Gersztenkorn discloses a modification of the Bahorich invention wherein a covariance matrix is determined for each of the cells and a seismic attribute determined from the eigenvalues of the covariance matrix is displayed. Gersztenkorn teaches that the ratio of the dominant eigenvalue of the covariance matrix to the sum of the eigenvalues is an indication of the coherence of the data. The presentation of these data is of a similarity measure on a time slice.
U.S. Pat. No. 6,055,482 to Sudhakar et al. teaches display of other types of seismic attributes in a 3-D data volume. For example, azimuth ordered seismic gathers are used to identify subterranean features such as fault and fracture patterns. Offset ordered coherence analysis is used to form an optimum stack at the subterranean location of interest.
A number of prior patents teach the use of color for displaying of seismic data to bring out features that are normally lost in a conventional seismic display. The teachings of U.S. Pat. No. 4,467,461 to Rice allow the interpreter to more easily comprehend simultaneous variation of several geophysical data attributes and to relate the effects to a specific end result for the geophysical indicators of interest. One or more geophysical attribute variables are quantified and then rasterized so that the data is represented as a gridded variable area display wherein color intensity of the grid units is some function of the instantaneous variable. The resulting data are then loaded into digital refresh memory of an image processing computer whereupon data are mixed for analysis in accordance with operator selected colors and color intensity weighting.
In U.S. Pat. No. 5,995,448 to Krehbiel, a suite of features extracted from a sequence of windows form a multivariate attribute of the raw data. These features include the energy, slope in the middle of a window, the autocorrelation, average trace amplitude, standard deviation of the amplitude, first and second lags of the autocorrelation. Combinations of three of these features are color coded and superimposed on a display of the seismic section.
U.S. Pat. No. 5,930,730 to Marfurt et al and Marfurt, K. J., Sudhaker, V., Gersztenkorn, A., Crawford, K. D. and Nissen, S. E., 1999, Coherency calculations in the presence of structural dip: Geophysics, Soc. of Expl. Geophys., 64, 104-111, teaches the use of color displays for a 3-D volume of seismic data. A color map, characterized by hue, saturation and lightness, is used to depict semblance/similarity, true dip azimuth and true dip of each cell; true dip azimuth is mapped onto the hue scale, true dip is mapped onto the saturation scale, and the largest measurement of semblance/similarity is mapped onto the lightness scale of the color map.
PCT Patent Publication WO 0014574 to Giertsen et al discloses a method of producing one or more volume windows within a 3-D data volume that can be interactively moved around in the entire data volume and viewed from different positions at different angles. By color and opacity manipulations inside the volume windows, the data therein are made transparent, allowing for visualization of selected target portions of the data set.
As pointed out in Giertsen, it is difficult to get a good understanding of complicated 3-D data set on a flat screen or a piece of paper. It is also laborious and difficult to interact with 3-D objects using a keyboard and a mouse. Analysis of 3-D data sets are commonly done using 2-D slices through the data cube. Furthermore, the screen size limits the amount of information that can be presented. Yet another drawback of prior methods of displaying 3-D data is that the interactive output of a graphical workstation is necessarily viewable only by a limited number of viewers.
The use of color displays in data presentation has increased with the advent of cost effective color display devices. Color displays have opened the door to the presentation of data in ways that have not been realized on standard displays. To people who can perceive colors, the added dimensions of color allow more detail to be placed on a display than can be placed on an equivalent gray scale. Color-additive and color-subtractive properties have been used by industry in an attempt to “see” features in multiattribute data sets. The number of possible schemes using these and other properties of color create presentation forms not possible using just shades of gray.
The potential increase in data density and the new presentation schemes present new problems to the interpreter. First, explorationists must learn the properties and merits of each new presentation scheme, the properties and merits must be discovered. Second, artifacts of the color display must be identified and removed from the interpretation. Features created by subtleties of variable-area wiggle-trace (VA+WT) displays can be recognized by explorationists. Color displays create more and varied artifacts. Finally, in order to recognize the merits and pitfalls of color displays, the explorationist should have a basic working knowledge of color theory. This knowledge need not be more than that found in an art class or encyclopedia, but should be sufficient to aid in differentiating between color artifacts and actual anomalies in the data.
Colors, when coming directly from light sources, blend to form different and brighter colors. All colors, when mixed together, produce a white light. This type of mixing, the same as produced by a color picture tube, is called color-addition. Colored reflectors, such as paints, do not behave this way when blended. Pigments, when mixed, produce darker colors; this is the color-subtractive property of color. Color can be broken into three components: hue, saturation, and lightness. The Munsell color system names the components “hue”, “chroma”, and “value”. The former terms to describe color-additive displays, the latter terms apply to color-subtractive based displays. The Munsell color system appears to be an ellipsoid with each axis representing one of the three components of color.
The three components of color can be used to produce several million different colors that the eye can differentiate. Hue contributes the basic coloring agent, such as red, green, or blue. Lightness or value is a measure of the brightness of the color. A gray-scale varies in lightness, from black (dark) to white (bright). Saturation or chroma is a measure of the proportion of hue to grayness. A gray-green would not be very saturated with color, yet a pure green would be saturated in color. No saturation would return us to the gray-scale.
A color variable density display of a seismic section has a different appearance than its black and white VA+WT counterpart. On a VA+WT display the apparent continuity of an event is generated by both the event's actual continuity and the amplitude of the event. The apparent continuity on a variable density display is composed of the actual continuity and the horizontal resolution. Low amplitude, but coherent, events are easier to spot on a variable density display than on a VA+WT display. The dynamic range of a black-and-white VA+WT display appears to be no more than 24 dB, a ratio of 16 to 1 between the largest amplitude value and the smallest discernible amplitude value. Most black-and-white variable density displays also have this range limitation. Through the use of color, it appears the effective dynamic range is around 30 to 36 dB, at least a doubling of the amplitude ratio. This not only allows representation of a wider range of amplitudes on a section, but also allows events that the processor has suppressed in amplitude to “reappear” on the section. For “relative-amplitude” displays this may be advantageous, but weak multiples and diffractions will reappear on the section. The standard VA+WT black-and-white section has a cut-off region for high amplitudes. When an event is of a high enough amplitude, it will start to overlap the adjacent trace. Thus, over a particular threshold it does not really matter what amplitude the trace is. This saturation effect is duplicated in a color display if amplitudes over a particular value are assigned a maximum color. Color also can display positive and negative amplitude values in a similar fashion, using two different hues.
The way in which the data is scaled to the various colors of the color bar can affect the appearance and interpretability of the display. Some schemes set the scaling by using the minimum and maximum data value, or some percentage of that value. Other schemes use a percentage of the data to set the minimum and maximum value, then linearly scale the color bar between these values. Still others control the percentage of data going to each color of the color bar. Each of these methods has advantages and drawbacks, but the advantages can not be realized unless a careful study of the color bar is made. If some portions of the color bar contain almost indistinguishable color variations, then assignment of an equal amount of data to each color will have little benefit. The scaling criteria for color displays is more critical than for black and white VA+WT displays and also creates more possibilities and problems.
The choice of colors in the color bar can affect the appearance of the display. For example, a color bar could be various shades of gray-green with a bright red color in the middle. The display resulting from the color bar will be composed of red bands, a red band occurring wherever the amplitude of the data passed through the red color range. The rest of the section will be fairly nondescript. This contouring of a particular amplitude range may have no geophysical meaning, but may be mapped and interpreted. Some color bars have this effect without assigning the drastic color changes to data value ranges of interest or significance. Others use this feature to accentuate the areas of interest. The colors in the color bar, and how they are applied, should be checked when looking at a color display.
Current commercially available 3D data presentation techniques for the petroleum exploration industry do not allow simultaneous display of information related to multiple geologic bedding planes (or features) without sacrificing display of information related to the relative or absolute sequencing of the planes (or features) to each other. Thus, only a limited amount of information can be presented to the interpreter or engineer in a single unified format, preventing the interpreter or engineer from making necessary associations, interpretations, or inferences to the multiple physical or geologic information available.
Heretofore, as is well known in the seismic processing and seismic interpretation arts and related geoscience disciplines, there has been a need for a method and apparatus for presenting and displaying (assimilation and visualization) more information characteristics simultaneously, about an object of interest, than current display methods provide for. Additionally, this method and apparatus should provide for improved attribute analyses and interpretation of data in one presentation. Accordingly, it should now be recognized, as was recognized by the present inventor, that there exists a need for a method and apparatus of data presentation, assimilation and visualization to address and solve the above-described problems.
Before proceeding to a description of the present invention, however, it should be noted and remembered that the description of the invention which follows, together with the accompanying drawings, should not be construed as limiting the invention to the examples (or preferred embodiments) shown and described. This is so because those skilled in the art to which the invention pertains will be able to devise other forms of this invention within the ambit of the appended claims.